1. Field of Invention
The invention relates generally to locking devices, and in particular, to the design and manufacture of locks.
2. Discussion of Related Art
A key-based lock is a mechanical fastening device which may be used on a door, vehicle, or container, for example, in order to prevent access to anyone without a correct key. Most modern locks employ a conventional “pin and tumbler” system to recognize when a correct key has been inserted into a lock. A conventional lock typically includes a plug (e.g., a cylinder) 20, a housing 22 (into which the plug fits) and a plurality of movable elements. Pairs of key pins and movable elements 28 (e.g., drive pins) are associated with one another. The pairs are disposed vertically with the key pin 26 below the moveable element 28 which engages the top of the key pin 26 in a shaft 30 which is present in the plug 20 and the housing 22. Springs in each shaft bias the associated moveable element 28 in the direction of the key pin 26. The moveable elements 28 push on the associated key pin 26 to maintain the position of the key pin 26 and the moveable element 28. Both the key pin 26 and the moveable element 28 may vary in length, however, in most conventional locks, the moveable elements 28 are typically all of the same length.
When no key is inserted in the conventional pin and tumbler lock, the key pin 26 is completely inside the plug 20, while the moveable element 28 is partially in the plug 20 and partially in the housing 22. The position of the moveable elements 28 keeps the plug 20 from turning (e.g., rotating). Thus, when no key (or the incorrect key) is inserted in the lock, the moveable elements 28 substantially fix the position of the plug 20 within the housing 22.
When a key is inserted in a conventional lock, the series of notches in the key push the pairs of key pins 26 and moveable elements 28 upward by varying amounts. An incorrect key moves at least one pair of key pins 26 and moveable elements 28 an incorrect amount such that either: 1) the pair is not moved far enough (i.e., the moveable element 28 continues to extend into both the housing 22 and the plug 20); or 2) the pair is moved too far upward (i.e., the key pin 26 extends into both the housing 22 and the plug 20).
A correct key moves each pair of key pins 26 and moveable elements 28 upward just enough so that an abutment surface occurring where the key pin 26 contacts the moveable element 28 aligns with the space where the plug 20 and the housing 22 meet (this boundary between the plug 20 and the housing 22 may be referred to as a shear line 38). Accordingly, a correct key moves the pairs of key pins 26 and moveable elements 28 into a position where all of the moveable elements 28 are inserted completely in the housing 22, while all of the key pins 26 rest completely in the plug 20. Thus, with no key pins 26 or moveable elements 28 interfering with a rotation of the plug 20 in the housing 22, the plug 20 rotates freely about an axis of rotation, and the bolt or locking device is able to move. Conventional locks are typically employed in a locking system where the plug 20 is mechanically connected to a cam, which in turn operates a spring to engage and disengage a latch.
Although locks are used for security purposes, the conventional lock may be opened without a key (e.g., the lock may be picked) thereby reducing or eliminating the effectiveness of the lock. Lock picking takes advantage of manufacturing tolerances and manufacturing defects present in virtually all conventional locks. These tolerances and defects allow the plug 20 to be rotated slightly in the housing 22 even when the lock is locked. Consequently, each moveable element 28 may rest on the shear line 38 when the abutment surface of a pair of key pins 26 and moveable elements 28 is aligned with the shear line 38 and the rotation of the plug 20 in the locked position is forced by an amount allowed by the manufacturing tolerance and/or defect. Lock pickers typically employ a tension wrench (i.e., a tensor) and a pick to pick a lock. In practice, the tension wrench is inserted into the keyhole and twisted slightly. The twisting of the wrench acts to rotate the plug 20 slightly, owing to the small spaces left in the shafts between the edges of the moveable elements 28 and the plug 20 (these are the manufacturing tolerances/defects referred to above). The rotation creates a ledge along the shear line 38 on which the moveable elements 28 can rest. The moveable element 28 rests on a ledge created by the portion of the outer surface of the plug 20 located at the radially inward end of the portion of the shaft 30 within the housing 22. The lock picker has in effect offset the portion of the shaft 30 in the housing 22 and the portion of the shaft 30 in the plug 20, i.e., the shaft in the housing 22 is no longer coaxially located with the shaft in the plug 20.
The pick is applied to each pair of key pins 26 and moveable elements 28 so that each moveable element 28 resides entirely within the housing 22 while resting on the ledges provided by the plug 20 at the shear line 38. The key pins 26 are then allowed to drop while a rotational force remains applied to the plug 20. If the proper amount of torque is applied, the key pins 26 fall back into the plug 20, while the Moveable elements 28 are caught on the ledge created by the slightly rotated plug 20. If this is accomplished, there are no longer any pins binding the plug 20 to the cylinder housing 22 and the plug can freely rotate as though the correct key had been used, i.e., the lock is unlocked.
Some known locks have been created with additional security features in an attempt to improve the security offered by the conventional lock designs. One such lock design is described in U.S. Pat. Nos. 5,289,709 and 6,718,807. The lock design described therein includes a side bar and rotating pins.
An example is illustrated in FIG. 1. Here, the key pins have a valley 54 cut into the side, and the bottom edges 56 of the key pins (the part that contacts the key) are not horizontal (as in most locks), but are instead beveled to a range of angles. The proper key also has beveled teeth designed to match the beveled edge of the key pin in such a way as to rotate the pins to the proper orientation. This rotation aligns the valleys in the side of the key pins with extensions 58 extending from the side bar 44. When the extensions do not lie in the valleys, the side bar is pushed out slightly, so that it lies between the plug and the cylinder housing. This prevents the plug from rotating, just as the pins do. When the pins are all rotated correctly, the protrusions from the side bar all lie in the valleys in the key pins, and the side bar moves out of the way, allowing the plug to rotate and the lock to open (assuming, of course, that the pins have been raised to the appropriate heights).
Although such designs may improve the security of the lock in view of some traditional lock-picking approaches, these designs may be successfully picked by employing other methods of lock picking. One such method, which has been reported, is the employment of a diamond rake bent at a 15 degree angle, which rakes both the pin heights and the pin rotations at the same time. Another reported method is the use of a bumping device which consists of a key with all its teeth cut to the maximum depth, whose beveling matches that of the correct key. The ‘bump key’ is then hit with some force to bump the key pins in the same manner as a lock gun, while holding the key pins at the correct rotational alignment. Thus, while these designs may increase the security of a lock, they may still be picked by an individual skilled in the craft of lock picking.
Another known variation in some conventional locks includes “mushroom” moveable elements, which, in one version, have a bottom that is shaped like an upside-down mushroom (other shapes are also possible for the “mushroom” moveable element, as shown at the top of FIG. 2). All these configurations are sometimes referred to, generally as “mushroom drivers.” In conventional locks with “mushroom” moveable elements, as shown in FIG. 2, the mushroom-shaped portion 28A of the moveable element 28 may get caught between the housing 22 and the plug 20 if too much torque is applied when picking. While these pins may make the picking process more difficult, they present only a marginal increase in difficulty, especially if one employs mechanical or electrical devices such as pick guns.